layout.js

registerLayout('my-grid-layout', class {
  static inputProperties = [/* etc */];

  constructor() {
    this.grid = []; // Place items on a cached grid so don't have to recompute each layout call.
  }

  addRemoveChildren(addRemoveList) {
    // Rebuild grid now, only occurs when child list changes.
    for (let i = 0; i < addRemoveList.length; i++) {
      this.grid[m][n] = child;
    }
  }
  
  layout(constraintSpace, breakToken, etc) {
    // Actually perform layout on the grid for the given constraint space.
  }
});